wasm-tracing-allocator

**A global allocator for Wasm that traces allocations and deallocations for
debugging purposes.**


wasm-tracing-allocator enables you to better debug and analyze memory leaks
and invalid frees in an environment where we don't have access to the
conventional tools like Valgrind. The tracing hooks are safely implemented in
JS, outside the Wasm module and its linear memory, to ensure that the tracing
code doesn't perturb results.

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* Enabling the Tracing Allocator
* Analyzing and Debugging

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First, add wasm-tracing-allocator to your Cargo.toml's dependency list:

``toml
[dependencies]
wasm-tracing-allocator = "0.1.0"
`

Next, configure wasm_tracing_allocator::WasmTracingAllocator as the global
allocator:

`rust
// src/lib.rs

use std::alloc::System;
use wasm_tracing_allocator::WasmTracingAllocator;

#[global_allocator]
static GLOBAL_ALLOCATOR: WasmTracingAllocator = WasmTracingAllocator(System);
`

Finally, make the JS implementations of the tracing hooks are available for your
Wasm module to import:

On the Web, add this script before* your Wasm module is instantiated:

`html

`

On Node.js, require the hooks before* your Wasm module is instantiated:

`js
require("wasm-tracing-allocator");
`

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Use your developer tools console to invoke methods of the global
WasmTracingAllocator object to get analyses about allocations and
deallocations.

The output is typically rendered with console.table:

![Example output](https://raw.githubusercontent.com/rustwasm/wasm-tracing-allocator/master/live-allocations-dump.png)

#### WasmTracingAllocator.dumpLiveAllocations

Dump a table of live allocations to the console.

`js
WasmTracingAllocator.dumpLiveAllocations({
keyLabel: String,
valueLabel: String,
getKey: Object => any,
getValue: Object => Number,
});
`

* keyLabel: Optional. The string label used to describe the keys column in the
table.

* valueLabel: Optional. The string label used to describe the values column in
the table.

* getKey: Optional. Function from an allocation entry object to anything. The
table will group and aggregate entries by their keys. Defaults to the stack at
the time of the allocation.

* getValue: Optional. Function from an allocation entry object to a
number. The values for all entries with the same key are summed. Defaults to
the byte size of each allocation; a potential alternative would be to ignore
the argument and return 1 to count the number of allocations instead.

#### WasmTracingAllocator.dumpInvalidFrees

Dump a table of invalid frees (double frees, frees of things that were never
allocated, etc...) to the console.

`js
WasmTracingAllocator.dumpInvalidFrees({
keyLabel: String,
valueLabel: String,
getKey: Object => any,
getValue: Object => Number,
});
`

* keyLabel: Optional. The string label used to describe the keys column in the
table.

* valueLabel: Optional. The string label used to describe the values column in
the table.

* getKey: Optional. Function from an invalid free entry object to anything. The
table will group and aggregate entries by their keys. Defaults to the stack at
the time of the deallocation.

* getValue`: Optional. Function from an invalid free entry object to a
number. The values for all entries with the same key are summed. Defaults to
counting the number of invalid frees.